Modeling max–min fair bandwidth allocation in BitTorrent communities

This paper gives an exact mathematical programming model and algorithm of the max–min fairness bandwidth allocation problem in multi-swarm peer-to-peer content sharing community. The proposed iterative method involves solution of LP and MILP problems of large scale. Based on real-world data traces, numerical experiments demonstrate that the new algorithm is computationally faster than an earlier developed one for larger problem sizes, and it provides better numerical stability. Moreover, even if its execution is stopped after some initial steps it still grants feasible solution with good approximation to max–min fairness.     

Basin Hopping Networks of continuous global optimization problems

Characterization of optimization problems with respect to their solvability is one of the focal points of many research projects in the field of global optimization. Our study contributes to these efforts with the usage of the computational and mathematical tools of network science. Given an optimization problem, a network formed by all the minima found by an optimization method can be constructed. In this paper we use the Basin Hopping method on well-known benchmarking problems and investigate the resulting networks using several measures.     

Hyperfine coupling dependence of the effects of weak magnetic fields on the recombination reactions of radicals generated from polymerisation photoinitiators

The recombination reactions of free radicals formed from the photolysis of a series of polymerisation photoinitiators were studied using time-resolved infrared spectroscopy. All molecules showed Zeeman magnetic field effects (MFEs) in the field range 0-37 mT and those molecules that produced radical pairs with average hyperfine couplings greater than 5 mT showed substantial inverted field effects at fields of less than 10 mT (so-called low field effects, LFEs). Monte Carlo simulations with full treatment of all the isotropic hyperfine couplings in the spin Hamiltonian reproduced well the observed field effects. The use of the usual analysis based on the calculated B1/2 value for the radical pair was found to be inappropriate in systems with substantial LFEs, but simple correlations between this B1/2 value and the observed field features were established.     

Description of the fluctuating colloid-polymer interface

To describe the full spectrum of surface fluctuations of the interface between phase-separated colloid-polymer mixtures from low scattering vector q (classical capillary wave theory) to high q (bulklike fluctuations), one must take account of the interface's bending rigidity. We find that the bending rigidity is negative and that on approach to the critical point it vanishes proportionally to the interfacial tension. Both features are in agreement with Monte Carlo simulations.     

The dependence of the radiative transition probability of donor-acceptor pairs on pair separation

The probability W(R) for radiative donor-acceptor pair transitions is generally assumed to decrease exponentially with increasing pair separation R, with a characteristic length a. When one centre in the pair is deep and strongly localized and the other one is shallow, a equals half the Bohr radius of the shallower centre. For pairs in GaP involving two shallow centres we have previously reported that a exceeds half this Bohr radius, and have suggested this to be due to the spatial extent of the deeper centre. In the present paper we investigate this point, both experimentally, and by considering Novotny's calculations — for direct transitions — on the R-dependence of W(R), in which the Bohr radii of both donor and acceptor are parameters. According to these calculations, W(R) is not exponential in the case of two shallow centres. In a limited range of R, W(R) is approximately exponential, however, and theoretical “effective values” of a can be obtained. These effective values are compared with experimental data on a for the pair series S_P-Si_P, S_P-Cd_Ga, S_P-Zn_Ga and S_P-C_P in the indirect semiconductor GaP; a amounts to ∽ 5.4, 7.0, 7.7 and 9.1 Å, respectively. The comparison shows that the difference found between the experimental a and half the Bohr radius of the less localized centre in the pair can indeed be explained by the influence on a of the spatial extent of the more localized centre. This findings implies a non-exponential W(R) for pairs with two shallow centres. This conclusion depends critically on the values used for the Bohr radii of the acceptors, however. These are not accurately known, due to insufficient knowledge of m¹_h, one of the quantities needed in calculating the radii. We used m¹_h = 0.36 m₀ to 0.40 m₀, corresponding to the normally used hydrogen-model energy of 40–45 meV. An alternative explanation for the experimental values of a is that in reality m¹_h is significantly lower than the 0.36 m₀ to 0.40 m₀ used, leading to larger acceptor Bohr radii and, in the extreme case, to no influence on a of the more localized centre and to an exponential W(R). In order to decide between the two possible explanations, additional experiments are presented. These include an accurate comparison of a between S_P-C_P and O_P-C_P as well as between S_P-Zn_Ga and O_P-Zn_Ga pairs. This is done by analysing the intergral band decay and time-resolved spectra of these pairs. The conclusions for all pairs mentioned are: (i) The Bohr radius of the acceptors involved is significantly larger than calculated from an effective-mass energy of 40–45 meV; they correspond to a hydrogen-model energy of 28 meV (m¹_h = 0.25 m₀). (ii) There is in first approximation no influence on the shape of W(R) of the spatial extent of the more localized centre. (iii) The experimental results are well described by an exponential W(R) with a equal to half the Bohr radius of the less localized centre of the pair.     

Recycling of crate material: Weatherability of stabilised recycled high density polyethylene

The uv stabilising effect of various stabilisers added to degraded, yellow-pigmented, high density polyethylene (HDPE) crate material originating from crates that have been in use for 10–13 years was investigated. For that purpose, outdoor and Xenotest-1200 exposure tests were carried out, and rates of oxygen absorption during photo-oxidation were determined. The uv stability of the degraded HDPE could be considerably improved—in particular, by the addition of a hindered amine type stabiliser (Tinuvin 770). The uv stability attainable is such that reuse of recycled crate material for the production of new crates is, after upgrading, a realistic possibility.A comparison of the results of outdoor and accelerated ageing showed that the acceleration factors strongly depend on the type of stabiliser applied. This can be attributed to the different mechanisms of stabilisation by which the various additives act.The uv stability of the recycled polymer appeared to be almost independent of the degree of degradation of the crates before recycling. This implies that it is not necessary to exclude from recycling heavily degraded crates which had failed due to brittle fracture.     

Influence of tryptophan loading on urinary excretion of anthranilic acid and 3-hydroxyanthranilic acid by men and women as determined by alkali flame ionization gas chromatography

A gas chromatographic method with alkali flame ionization detection is described for the determination of urinary total (free and conjugated) anthranilic acid (AA) and 3-hydroxyanthranilic acid (HAA) as their pentafluorobenzyl esters. Prior to analysis, urine was hydrolysed using hydrochloric acid in a boiling water bath. The highest AA and HAA yields were obtained with 4 M hydrochloric acid and a hydrolysis time of 4 h. The coefficients of variation of the between-run analyses of AA and HAA at the endogenous level were 7.2 and 5.8%, respectively. The average recovery for both substances was 84%. The method described has been used to study the excretion of AA and HAA in the urine of healthy males and females before and after an oral load of tryptophan. Furthermore, the influence of oral contraceptives has been investigated. Results indicate that for both sexes the excretion of AA in the urine was higher than that of HAA, except after tryptophan loading. The excretion of AA by women was higher than by men. For HAA, the results of both sexes were comparable. Furthermore, for neither of the sexes was a diurnal variation of AA or HAA observed. After tryptophan loading, the formation of HAA was increased by more than that of AA. Results obtained for women on oral contraceptives indicate a hormonal-induced inhibition of AA formation.     

The photo-oxidation of polyolefins containing a hindered piperidine compound

The rate of oxygen absorption by unstabilised PE and PP, as well as by the same polymers stabilised with bis-(2,2,6,6-tetramethyl-4-piperidinyl) sebacate (Tinuvin 770), has been determined during photo-oxidation at several temperatures and uv light intensities. In addition, the rate of stabiliser conversion has been measured under various irradiation conditions, including outdoor exposure. The activation energy of the conversion of Tinuvin 770 appears to be much less than that of the photo-oxidation of PE. When stabilised with 0·1% Tinuvin 770, PE and PP differ with respect to the dependence on light intensity of their rates of oxygen uptake. The consequences of these results for the interpretation of accelerated ageing tests are discussed.     

Applications of life cycle assessment to NatureWorks™ polylactide (PLA) production

NatureWorks™ polylactide (PLA)¹ is a versatile polymer produced by Cargill Dow LLC. Cargill Dow is building a global platform of sustainable polymers and chemicals entirely made from renewable resources. Cargill Dow's business philosophy is explained including the role of life cycle assessment (LCA), a tool used for measuring environmental sustainability and identifying environmental performance-improvement objectives. The paper gives an overview of applications of LCA to PLA production and provides insight into how they are utilized. The first application reviews the contributions to the gross fossil energy requirement for PLA (54 MJ/kg). In the second one PLA is compared with petrochemical-based polymers using fossil energy use, global warming and water use as the three impact indicators. The last application gives more details about the potential reductions in energy use and greenhouse gasses. Cargill Dow's 5–8 year objective is to decrease the fossil energy use from 54 MJ/kg PLA down to about 7 MJ/kg PLA. The objective for greenhouse gasses is a reduction from +1.8 down to −1.7 kg CO₂ equivalents/kg PLA.     

Synthesis of functionalized dna fragments suitable for reversible attachment to activated cellulose

A system consisting of donor (1), template (2) and immobilized acceptor molecules (58,59,64-67) which may be used for an enzymatic extension (T4 DNA ligase) of immobilized DNA fragments is described. The synthesis of the donor (1), template (2) and the functionalized acceptor molecules (3-8) was performed via phosphotriester intermediates. The functionalized acceptor molecules used in this study contained: base labile bonds (i.e. compounds 3-6), an acid labile bond (i.e. compound 7) or a RNase labile bond (i.e. compound 8). The functionalized acceptor molecules (3,4) could be immobilized to cellulose activated with 2,4,6-trichloro-s-triazine and the other molecules (5-8) to 2-amino-4, 6-dichloro-s-triazine to give the immobilized DNA complexes 58, 59 and 64-67, respectively, in high yield. The immobilized DNA fragments could be released quantitatively from the solid support by: base treatment (i.e. 58, 59, 64 and 65 gave DNA-fragments 60, 61, 68 and 69 respectively), acid treatment (i.e. 66 gave DNA-fragment 70) or RNase digestion (i.e. 67 gave deoxythymidine).